Fundamental research on twofold phase formation of apatite solid-solutions and leucite in glass-ceramics

Abstract

In this study the phase formation of apatites in the multi-component SiO₂-Al₂O₃-Na₂O-K₂O-GaO/SrO-P₂O₅-F system was investigated. Based on a special composition GaO was partially and completely substituted by SrO. Room and high temperature X-ray diffraction (RT- and HT-XRD) and scanning electron microscopy (SEM) were used to characterize the phase formation. The results of this study showed a formation of two different apatite solid-solutions, Sr_(7.3)Ca_(2.7)(PO₄)₆F₂ and Sr₆Ca₄(PO₄)₆F₂ and Sr-apatite Sr₅(PO₄)₃F. Leucite formation is based on surface crystallization. The conclusion is a twofold volume and surface nucleation and crystallization mechanism.